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- Use RIP instead of X86_PF_INSTR for vsyscall emulation 

- Remove ENDBR64 from FRED entry points
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Merge tag 'x86_entry_for_6.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 entry updates from Dave Hansen:
 "A pair of x86/entry updates.

  The FRED one adjusts the kernel to the latest spec. The spec change
  prevents attackers from abusing kernel entry points.

  The second one came about because of the LASS work[1]. It moves the
  vsyscall emulation code away from depending on X86_PF_INSTR which is
  not available on some CPUs. Those CPUs are pretty obscure these days,
  but this still seems like the right thing to do. It also makes this
  code consistent with some things that the LASS code is going to do.

   - Use RIP instead of X86_PF_INSTR for vsyscall emulation

   - Remove ENDBR64 from FRED entry points"

Link: https://lore.kernel.org/lkml/20250620135325.3300848-1-kirill.shutemov@linux.intel.com/ [1]

* tag 'x86_entry_for_6.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/fred: Remove ENDBR64 from FRED entry points
  x86/vsyscall: Do not require X86_PF_INSTR to emulate vsyscall
This commit is contained in:
Linus Torvalds 2025-10-04 10:25:22 -07:00
parent be786eba12 3da01ffe1a
commit 7c738cb4ca
2 changed files with 15 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/entry/entry_64_fred.S
View File

@ -16,7 +16,7 @@
.macro FRED_ENTER
UNWIND_HINT_END_OF_STACK
ENDBR
ANNOTATE_NOENDBR
PUSH_AND_CLEAR_REGS
movq %rsp, %rdi /* %rdi -> pt_regs */
.endm

17
arch/x86/entry/vsyscall/vsyscall_64.c
View File

@ -124,7 +124,12 @@ bool emulate_vsyscall(unsigned long error_code,
if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
return false;
if (!(error_code & X86_PF_INSTR)) {
/*
* Assume that faults at regs->ip are because of an
* instruction fetch. Return early and avoid
* emulation for faults during data accesses:
*/
if (address != regs->ip) {
/* Failed vsyscall read */
if (vsyscall_mode == EMULATE)
return false;
@ -136,13 +141,19 @@ bool emulate_vsyscall(unsigned long error_code,
return false;
}
/*
* X86_PF_INSTR is only set when NX is supported. When
* available, use it to double-check that the emulation code
* is only being used for instruction fetches:
*/
if (cpu_feature_enabled(X86_FEATURE_NX))
WARN_ON_ONCE(!(error_code & X86_PF_INSTR));
/*
* No point in checking CS -- the only way to get here is a user mode
* trap to a high address, which means that we're in 64-bit user code.
*/
WARN_ON_ONCE(address != regs->ip);
if (vsyscall_mode == NONE) {
warn_bad_vsyscall(KERN_INFO, regs,
"vsyscall attempted with vsyscall=none");